Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes.
Ink sticks currently in use are typically manufactured with a formed tub and flow fill process. In this method, the component dyes and carrier composition are heated to their liquid state and then poured into a tub having an interior shape corresponding to the desired finished ink stick shape. The tub may also be formed with indentations and protrusions for forming keying and coding features in the ink sticks, if desired. This manufacturing method allows formation of non-linear shapes but occasionally produces peripheral shapes with poor tolerance control and poor control of stick height, or axis of fill. Inadequate height control and stress cracks may be caused by non uniform cooling, particularly with irregularly shaped ink sticks. Specifically, the outer layer of the molten ink and carrier radiate heat to the outside air and cool more quickly than the interior portions of the mixture. Therefore, protrusions from the main body of the ink material may cool more quickly and be susceptible to breaking off and cracking.
Additionally, features cannot be formed in the upper surface with this method because of the open top of the tub. Due to the open top of the forming tub, the top surface of the ink material may solidify lacking planarity or the top surface may solidify too quickly and crack. The top surface nearly always solidifies into an uncontrolled, not flat shape such that stick to stick and areas across a stick vary in height. Poor height control can allow sticks to be undesirably displaced during handling and transport and even operation of the printer or imaging device. The flow fill process has been used in spite of these limitations because it is relatively fast and cost effective.